Abstract

In this letter, we investigate the upconversion properties of glass after excitation into the level using 980 nm radiation. At an excitation power density of 880 W/cm2, green emission dominates the upconversion spectrum with an efficiency of 0.16%. Temporal studies reveal that the level is the intermediate state by which the two-step upconversion process occurs. Excited-state absorption and phonon-assisted energy transfer are discussed as possible mechanisms for the upconversion.